As digital image photographing apparatuses, such as digital still cameras and mobile phones having a camera function, gain popularity, hard discs and other recording media for recording photographed images have become available inexpensively.
Generally, users of digital image photographing apparatuses and the like (hereinafter simply referred to as users) store photographed images on a recording medium such as a hard disc with a large capacity.
If the number of stored images grows large, users have difficulty searching for a particular image. To facilitate searching, images may be classified into categories. For example, images photographed at an athletic meet are classified into a category “athletic meet.”
An example of technology for classifying images is to calculate, from each stored image, image feature information indicating a feature of the image and classify images into categories using the calculated image feature information, as described in Patent Literature 1. Another known form of technology is to classify images using the number of and sizes of faces appearing in each image, as described in Patent Literature 2.